MPLS Encapsulation for SFC NSH
draft-malis-mpls-sfc-encapsulation-01

SFC Working Group                                               A. Malis
Internet-Draft                                                 S. Bryant
Intended status: Informational                       Huawei Technologies
Expires: December 30, 2018                                    J. Halpern
                                                                Ericsson
                                                           W. Henderickx
                                                                   Nokia
                                                           June 28, 2018

                     MPLS Encapsulation for SFC NSH
                 draft-malis-mpls-sfc-encapsulation-01

Abstract

   This document describes how to use a Service Function Forwarder (SFF)
   Label (similar to a pseudowire label or VPN label) to indicate the
   presence of a Service Function Chaining (SFC) Network Service Header
   (NSH) between an MPLS label stack and the packet payload.  This
   allows SFC packets using the NSH to be forwarded between SFFs over an
   MPLS network, and the selection between multiple SFFs in the
   destination MPLS node.

Status of This Memo

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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  MPLS Encapsulation Using an SFF Label . . . . . . . . . . . .   3
     2.1.  MPLS Label Stack Construction . . . . . . . . . . . . . .   3
   3.  ECMP Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Operations, Administration, and Maintenance (OAM)
       Considerations  . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   As discussed in [RFC8300], a number of transport encapsulations for
   the Service Function Chaining (SFC) Network Service Header (NSH)
   already exist, such as Ethernet, GRE [RFC2784], and VXLAN-GPE
   [I-D.ietf-nvo3-vxlan-gpe].

   This document describes an MPLS transport encapsulation for the NSH,
   and also describes how to use a Service Function Forwarder (SFF)
   [RFC7665] Label to indicate the presence of the NSH in the MPLS
   packet payload.  This allows SFC packets using the NSH to be
   forwarded between SFFs in an MPLS transport network, where MPLS is
   used to interconnect the network nodes that contain one or more SFFs.
   The label is also used to select between multiple SFFs in the
   destination MPLS node.

   SFF Labels are similar to other service labels at the bottom of an
   MPLS label stack that denote the contents of the MPLS payload being
   other than IP, such as a layer 2 pseudowire, an IP packet that is
   routed in a VPN context with a private address, or an Ethernet
   virtual private wire service.

   This informational document follows well-established MPLS procedures
   and does not require any actions by IANA or any new protocol
   extensions.

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2.  MPLS Encapsulation Using an SFF Label

   The encapsulation is a standard MPLS label stack [RFC3032] with an
   SFF Label at the bottom of the stack, followed by a NSH as defined by
   [RFC8300] and the NSH payload.

   Much like a pseudowire label, an SFF Label is allocated by the
   downstream receiver of the NSH from its per-platform label space.

   If a receiving node supports more than one SFF (i.e, more than one
   SFC forwarding instance), then the SFF Label can be used to select
   the proper SFF, by having the receiving advertise more than one SFF
   Label to its upstream sending nodes as appropriate.

   The method used by the downstream receiving node to advertise SFF
   Labels to the upstream sending node is out of scope of this document.
   That said, a number of methods are possible, such as via a protocol
   exchange, or via a controller that manages both the sender and the
   receiver using NETCONF/YANG, BGP, PCEP, etc.  These are meant as
   possible examples and not to constrain the future definition of such
   advertisement methods.

2.1.  MPLS Label Stack Construction

   When one SFF wishes to send an SFC packet with the NSF to another SFF
   over an MPLS transport network, a label stack needs to be constructed
   by the MPLS node that contains the sending SFF in order to transport
   the packet to the destination MPLS node that contains the receiving
   SFF.  The label can be constructed as follows:

   1.  Push on zero or more labels that are interpreted by the
       destination MPLS node, such as the Generic Associated Channel
       [RFC5586] label (see OAM Considerations below).

   2.  Push on the SFF Label to identify the desired SFF in the
       receiving MPLS node.

   3.  Push on zero or more additional labels such that (a) the
       resulting label stack will cause the packet to be transported to
       the destination MPLS node, and (b) when the packet arrives at the
       destination node, either:

       *  the SFF Label will be at the top of the label stack, or

       *  the SFF Label will rise to the top of the label stack before
          the packet is forwarded to another node and before the packet
          is dispatched to a higher layer.

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   The receiving MPLS node pops the NSH Label (and any labels beneath
   it) so that the destination SFF receives the SFC packet with the NSH
   is at the top of the packet.

3.  ECMP Considerations

   As discussed in [RFC4928] and [RFC7325], there are Equal Cost
   Multipath (ECMP) considerations for payloads carried by MPLS.  Many
   existing routers use deep packet inspection to examine the payload of
   an MPLS packet, and if the first nibble of the payload is equal to
   0x4 or 0x6, these routers assume that the payload is IPv4 or IPv6
   respectively, and perform ECMP load balancing on the MPLS packets.

   For SFC, ECMP may or may not be desirable.  To prevent unintended
   ECMP when it is not desired, the NSH Base Header was carefully
   constructed so that the NSH could not look like IPv4 or IPv6 based on
   its first nibble.  See Section 2.2 of [RFC8300] for further details.

   If ECMP is desired when SFC is used with an MPLS transport network,
   there are two possible options, Entropy [RFC6790] and Flow-Aware
   Transport [RFC6391] labels.  A recommendation between these options,
   and their proper placement in the label stack, is for future study.

4.  Operations, Administration, and Maintenance (OAM) Considerations

   OAM at the SFC Layer is handled by SFC-defined mechanisms [RFC8300].
   However, OAM may be required at the MPLS transport layer.  If so,
   then standard MPLS-layer OAM mechanisms such as the Generic
   Associated Channel [RFC5586] label may be used.

5.  IANA Considerations

   This document does not request any actions from IANA.

   Editorial note to RFC Editor: This section may be removed at your
   discretion.

6.  Security Considerations

   This document describes a method for transporting SFC packets using
   the NSH over an MPLS transport network.  It follows well-established
   MPLS procedures and does not define any new protocol elements or
   allocate any new code points.  It is therefore operationally
   equivalent to other existing SFC transport encapsulations as defined
   in [RFC8300].  As such, it should have no effect on SFC security as
   already discussed in Section 8 of [RFC8300].

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7.  Acknowledgements

   The authors would like to thank Jim Guichard, Eric Rosen, Med
   Boucadair, and Sasha Vainshtein for their reviews and comments.

8.  References

8.1.  Normative References

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
              <https://www.rfc-editor.org/info/rfc3032>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

8.2.  Informative References

   [I-D.ietf-nvo3-vxlan-gpe]
              Maino, F., Kreeger, L., and U. Elzur, "Generic Protocol
              Extension for VXLAN", draft-ietf-nvo3-vxlan-gpe-06 (work
              in progress), April 2018.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              DOI 10.17487/RFC2784, March 2000,
              <https://www.rfc-editor.org/info/rfc2784>.

   [RFC4928]  Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
              Cost Multipath Treatment in MPLS Networks", BCP 128,
              RFC 4928, DOI 10.17487/RFC4928, June 2007,
              <https://www.rfc-editor.org/info/rfc4928>.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,
              <https://www.rfc-editor.org/info/rfc5586>.

   [RFC6391]  Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V.,
              Regan, J., and S. Amante, "Flow-Aware Transport of
              Pseudowires over an MPLS Packet Switched Network",
              RFC 6391, DOI 10.17487/RFC6391, November 2011,
              <https://www.rfc-editor.org/info/rfc6391>.

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   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [RFC7325]  Villamizar, C., Ed., Kompella, K., Amante, S., Malis, A.,
              and C. Pignataro, "MPLS Forwarding Compliance and
              Performance Requirements", RFC 7325, DOI 10.17487/RFC7325,
              August 2014, <https://www.rfc-editor.org/info/rfc7325>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.

Authors' Addresses

   Andrew G. Malis
   Huawei Technologies

   Email: agmalis@gmail.com

   Stewart Bryant
   Huawei Technologies

   Email: stewart.bryant@gmail.com

   Joel M. Halpern
   Ericsson

   Email: joel.halpern@ericsson.com

   Wim Henderickx
   Nokia

   Email: wim.henderickx@nokia.com

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